/*
 * Copyright (c) 2016, Linaro Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its contributors
 * may be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#include <stdlib.h>
#include <unistd.h>

#include "hdlc.h"
#include "util.h"

/*
 * HDLC frame check is performed by a reversed CRC-CCITT-16 with polynomial
 * x^16 + x^12 + x^5 + 1 (0x8408), an initial value of 0xffff and the result
 * XORed with 0xffff.
 *
 * Calculation is performed with a table lookup as described in
 * http://www.ross.net/crc/download/crc_v3.txt
 */
static uint16_t crc_table[256] = {
	0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48,
	0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108,
	0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb,
	0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399,
	0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e,
	0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e,
	0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd,
	0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
	0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285,
	0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44,
	0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f, 0x4014,
	0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5,
	0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3,
	0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862,
	0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e,
	0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
	0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1,
	0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483,
	0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50,
	0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710,
	0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7,
	0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1,
	0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72,
	0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
	0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e,
	0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf,
	0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d,
	0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
	0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

static uint16_t hdlc_crc_byte(uint16_t crc, uint8_t ch)
{
	return (crc >> 8) ^ crc_table[(crc ^ ch) & 0xff];
}

void *hdlc_encode(const void *src, size_t slen, size_t *dlen)
{
	const uint8_t *end = src + slen;
	const uint8_t *s = src;
	uint16_t crc = 0xffff;
	uint8_t tmp[2];
	uint8_t *dst;
	uint8_t *d;
	int i;

	dst = malloc((slen + 2) * 2 + 1);
	if (!dst)
		return NULL;

	d = dst;
	while (s < end) {
		crc = hdlc_crc_byte(crc, *s);

		if (*s == 0x7d || *s == 0x7e) {
			*d++ = 0x7d;
			*d++ = *s++ ^ 0x20;
		} else {
			*d++ = *s++;
		}
	}

	tmp[0] = ~crc & 0xff;
	tmp[1] = ~crc >> 8;

	s = tmp;
	for (i = 0; i < 2; i++) {
		if (*s == 0x7d || *s == 0x7e) {
			*d++ = 0x7d;
			*d++ = *s++ ^ 0x20;
		} else {
			*d++ = *s++;
		}
	}

	*d++ = 0x7e;
	*dlen = d - dst;

	return dst;
}

void *hdlc_decode_one(struct hdlc_decoder *hdlc, struct circ_buf *buf,
		      size_t *msglen)
{
	uint8_t ch;

	if (!hdlc->raw)
		hdlc->raw = hdlc->raw_buf;

	for (;;) {
		if (buf->tail == buf->head)
			return 0;

		ch = buf->buf[buf->tail];
		buf->tail = (buf->tail + 1) & (HDLC_BUF_SIZE - 1);

		if (ch == 0x7e) {
			break;
		} else if (ch == 0x7d) {
			hdlc->escape = 0x20;
		} else {
			*hdlc->raw++ = ch ^ hdlc->escape;
			hdlc->escape = 0;
		}

	}

	if (hdlc->raw == hdlc->raw_buf)
		return NULL;

	hdlc->raw--;
	hdlc->raw--;

	*msglen = hdlc->raw - hdlc->raw_buf;

	hdlc->raw = hdlc->raw_buf;
	hdlc->escape = 0;

	return hdlc->raw_buf;
}
